Emission Switching Research Articles

Synthesis, characterization and emission switching behaviors of styrylphenyl-conjugated Ru(II)-terpyridine complexes via aggregation and trans–cis photoisomerization

An array of styrylphenyl-conjugated Ru(II)-terpyridine complexes have been designed and detailed investigation of their photophysical and electrochemical characteristics have been carried off. The compounds by virtue of the presence of polyaromatic units exhibit both aggregation-induced emission quenching and enhancement. Styrylphenyl units allow the trans–trans to trans–cis photoisomerization in the free- as well as aggregated form of the complexes upon irradiation with visible light which can be reverted back by shining with UV light. Hence, “on–off” and “off–on” switching of emission occurs upon consecutive treatment of complexes with different light sources. The rate constant and quantum yield of photoisomerization in both free and aggregated forms have been calculated and is found to decrease upon increase in extent of aggregation. Theoretical analysis through density functional theory (DFT) and time-dependent DFT methods was also carried out for appropriate band assignment and to have some insight for the occurrence of photoisomerization process.

Reversible Luminescent Switching Induced by Heat/Water Treatment in a Zero-Dimensional Hybrid Antimony(Ⅲ) Chloride.

Recently zero-dimensional (0-D) inorganic-organic metal halides (IOMHs) have become a promising class of optoelectronic materials. Herein, we report a new photoluminescent (PL) 0-D antimony(III)-based IOMH single crystal, namely [H2BPZ][SbCl5]·H2O (BPZ = benzylpiperazine). Photophysical characterizations indicate that [H2BPZ][SbCl5]·H2O exhibits singlet/triplet dual-band emission. Density functional theory (DFT) calculations suggest that [H2BPZ][SbCl5]·H2O has the large energy difference between singlet and triplet states, which might induce the dual emission in this compound. Temperature-dependent PL spectra analyses suggest the soft lattice and strong electron-phonon coupling in this compound. Thermogravimetric analysis shows that the water molecules in the lattice of the title crystal could be removed by thermal treatment, giving rise to a dehydrated phase of [H2BPZ][SbCl5]. Interestingly, such structural transformation is accompanied by a reversible PL emission transition between red light (630 nm, dehydrated phase) and yellow light (595 nm, water-containing phase). When being exposed to an environment with 77% relative humidity, the emission color of the dehydrated phase was able to change from red to yellow within 20 s, and the red emission could be restored after reheating. The red to yellow emission switching could be achieved in acetone with water concentration as low as 0.2 vol%. The reversible PL transition phenomenon makes [H2BPZ][SbCl5]·H2O a potential material for luminescent water-sensing.

Fluorescence-Activating and Absorption-Shifting Nanoprobes for Anaerobic Tracking of Gut Microbiota Derived Vesicles.

Outer membrane vesicles (OMVs) are crucial for bacterial intercellular communication and the crosstalk between the gut microbiota and its host. Methods capable of visualizing gut microbiota derived OMVs would be of great significance but have been rarely reported. Here, nanoprobes carrying a fluorescence-activating and absorption-shifting tag are prepared by combining genetic engineering and antibiotic-boosted vesicle formation and release. Benefiting from their natural structure and molecular oxygen-independent emission, the resulting nanovesicles can be applied as endogenous fluorescence probes to anaerobically track gut microbiota associated OMVs. These nanoprobes show flexibility in on-demand fluorescence turn-on/off and reversibly switchable emission bands for intelligent and dual-color imaging. With these special characteristics, the behaviors of microbiota OMVs to not only inhibit specific pathogenic strains through membrane fusion but also repair the intestinal barrier via entering intestinal epithelia and promoting the expressions of tight junctions are tracked and identified in the gut. Based on these discoveries, OMVs are disclosed to be able to remit inflammation in a murine model of colitis following transplantation to the intestine by oral delivery. This work provides an approach to visualize the dynamics of the gut microbiota and disclose potential targets for disease intervention.

Mechanochromic Materials Based on Tetraphenylethylene-Substituted Phenothiazines: Substituent-Dependent Hypsochromic and Bathochromic Switching of Emission

Phenothiazine- and tetraphenylethylene (TPE)-based mechanochromic materials (PTZTPE-1CHO, PTZTPE-4CHO, and PTZTPE-4CN) with different electron-withdrawing substituents (−CHO and −CN) were designed and synthesized by the Suzuki cross-coupling reaction of bromo-TPEs with the corresponding boronate esters of phenothiazine. The photophysical, aggregation-induced emission, mechanochromic, thermal, and electroluminescence properties of the synthesized compounds were investigated. The cyano group-bearing derivative PTZTPE-4CN exhibited reversible mechanochromism, and its emission maximum shifted bathochromically when mechanically ground, whereas the formyl group-containing derivatives PTZTPE-1CHO and PTZTPE-4CHO exhibited hypsochromically shifted mechanochromism. The solution of PTZTPE-4CN was weakly emissive, and PTZTPE-1CHO and PTZTPE-4CHO exhibit strong fluorescence in the solution state due to the intramolecular charge transfer transitions. The electroluminescence properties of the synthesized compounds as non-annealed and annealed non-doped prompt fluorescent emitters were studied in organic light-emitting diodes, which showed a maximum external quantum efficiency of 1.2% and a luminance of 8762 cd·m–2.

Photo-controllable Luminescence from Radicals Leading to Ratiometric Emission Switching via Dynamic Intermolecular Coupling.

The development of photoinduced luminescent radicals with dynamic emission color is still challenging. Herein we report a novel molecular radical system (TBIQ) that shows photo-controllable luminescence, leading to a wide range of ratiometric color changes via light excitation. The conjugated skeleton of TBIQ is decorated with steric-demanding tertiary butyl groups that enable appropriate intermolecular interaction to make dynamic intermolecular coupling possible for controllable behaviors. We reveal that the helicenic pseudo-planar conformation of TBIQ experiences a planarization process after light excitation, leading to more compactly stacked supermolecules and thus generating radicals via intermolecular charge transfer. The photo-controllable luminescent radical system is employed for a high-level information encryption application. This study may offer unique insight into molecular dynamic motion for optical manufacturing and broaden the scope of smart-responsive materials for advanced applications.

Photo‐controllable Luminescence from Radicals Leading to Ratiometric Emission Switching via Dynamic Intermolecular Coupling

AbstractThe development of photoinduced luminescent radicals with dynamic emission color is still challenging. Herein we report a novel molecular radical system (TBIQ) that shows photo‐controllable luminescence, leading to a wide range of ratiometric color changes via light excitation. The conjugated skeleton of TBIQ is decorated with steric‐demanding tertiary butyl groups that enable appropriate intermolecular interaction to make dynamic intermolecular coupling possible for controllable behaviors. We reveal that the helicenic pseudo‐planar conformation of TBIQ experiences a planarization process after light excitation, leading to more compactly stacked supermolecules and thus generating radicals via intermolecular charge transfer. The photo‐controllable luminescent radical system is employed for a high‐level information encryption application. This study may offer unique insight into molecular dynamic motion for optical manufacturing and broaden the scope of smart‐responsive materials for advanced applications.

Tuning the 1D-2D dimensionality upon ligand exchange in silver thiolate coordination polymers with photoemission switching.

Silver nanoparticles are known and widely used for their antimicrobial activities. Nevertheless, once they are released into the natural or biological environments, they can become toxic with time, because of the dissolution of some Ag(I) ions that can then react with thiol-based molecules, such as glutathione and/or compete with copper proteins. These assumptions are based on the high affinity of the soft acid Ag(I) and the soft base thiolates and the exchange reactions that are involved in complex physiological media. Here we synthesized and fully characterized two new 2D silver thiolate coordination polymers (CPs) that exhibit a reversible 2D-to-1D structural transformation in the presence of an excess of thiol molecules. This dimensionality change induces also a switch of the yellow emission of the Ag-thiolate CP. This study highlights that these highly stable silver-thiolate CPs, in basic, acidic and oxidant media can undergo a complete dissolution-recrystallization mechanism upon thiol exchange reactions.

Spirocyclic rhodamine B benzoisothiazole derivative: a multi-stimuli fluorescent switch manifesting ethanol-responsiveness, photo responsiveness, and acidochromism.

Multi-stimuli fluorescent switching materials have been extensively employed in chemistry, biochemistry, physics, and materials science. Although rhodamine-based spirolactams have been specifically considered for metal ion sensing by photoluminescence, only some of them manifest photochromic behavior, and further development of rhodamine B (RHB)-based photochromic materials is required. RHB and its cyclic amides are advantageous in various sensing applications owing to their colorimetric responses to external stimulation. Hence, the current work reports a novel multifunctional active molecular material (3',6'-bis(diethylamino))-2-(5-nitrobenzo[c]isothiazol-3-yl)spiro[isoindoline-1,9'-xanthen]-3-one (RHBIT) by linking rhodamine B with 3-amino,5-nitro[2,1]benzoisothiazole (ANB) in a facile synthetic pathway; that perceives both emission color change and switching between off-on states. RHBIT shows acidochromism, photochromism, and pH sensitivity accompanied by unique ethanol responsiveness, with potential applications in anti-counterfeiting and drug delivery. Notably, RHBIT is highly acid sensitive and reverts to the ring-closed form on treatment with triethylamine (base), visible with the naked eye amidst colorless-pink-colorless transformations. On short UV irradiation, RHBIT provides a two-fold rise in the lifetime for the ring-open form in CHCl3 and DCM compared to the spirolactam (closed form). DFT and TDDFT studies provide electronic characterization for the absorption spectra of the open and closed forms. Using the photoresponsive feature of RHBIT, an information protection application has been enacted via a rewritable platform.

Flanking-donor-controlled diversity in mechanical-force-induced reversible fluorochromism and enhanced emission for carboxylic acid and ester linked solid-state emitters

Flanking donor-controlled diverse mechano-induced emission switching (MFC) and enhanced emission (MIEE).

Near-infrared emission, energy transfer, and mechanisms of Mn2+ and Cr3+ Co-doped lead-free Cs2AgInCl6 double perovskites

Mn2+/Cr3+ codoped Cs2AgInCl6 double perovskite were synthesized via a facile hydrothermal method, which exhibits two photoluminescence bands with a wide emission switch ranging from orange to NIR and the photoluminescence quantum yield of 49.3%.

Chirality Transfer from Polylactide to Achiral Fluorophore in Hierarchical Crystallization for Realizing Handedness-Tunable and Nonreciprocal Circularly Polarized Luminescence

Realizing chiral crystals from achiral compounds is an important but challenging issue. Here, a kebab-structured chiral supra-crystallization complex is constructed in accomplishing hierarchical chiral crystallization of achiral fluorescent compound (1,8-naphthalic anhydride, NA) employing synthetic chiral macromolecules (polylactide, PLA) as a template. Chirality transfer efficiently takes place from PLA to NA crystal during the co-crystallization process, endowing the initial achiral NA crystal with intense optical activity. More importantly, the obtained chiral supra-crystals show remarkable circularly polarized luminescence (CPL) properties, with the highest luminescence dissymmetric factor up to 5 × 10–2. Moreover, handedness-tunable and nonreciprocal CPL emissions are further realized in one single sample by simply flipping and rotating the supra-crystallization composite film, following a polarization mechanism. The work presents the first polymer-based hierarchical chiral supra-crystal with switchable CPL emissions and provides a simple and universal strategy for constructing nonreciprocal CPL materials.

Simulation for Distributions of Several Geometric Parameters in Nulling Pulsars

We investigate the distributions of the obliquity angle and impact parameters of nulling pulsars of different duty cycles based on the simulation of more than 600,000 samples. We adopt a purely geometric approach for pulsar visibility, in which visible emission is emitted tangentially to the magnetic field line and parallel to the line-of-sight direction. The geometry is incorporated with the model for pulsar magnetospheres of multiple emission states, in which the plasma charge density is dependent on the emission state. We assume that an emission state can only exist between two limiting conditions described by the vacuum and corotation models, respectively. In this model, pulse nulling corresponds to emission switching to a state in which the plasma charge density is zero. The event is detectable only if the switching occurs at source points that lie on a trajectory, whose locus defines the locations of visible emission, within an open-field region. Our results show that detectable nulling is dependent on all three parameters, such that nulling pulsars prefer a small obliquity angle and duty cycle, and tend to have positive impact parameters. We find that the total population of nulling pulsars in our samples is around 23%, of which about 47% possess a duty cycle of 0.1 or smaller. The former implies that there are more nulling pulsars than currently known. Our model predicts that the number of nulling pulsars increases as the obliquity angle decreases, which also implies that the occurrence of nulling in a pulsar should evolve over time.

Dynamic B/N Lewis Pairs: Insights into the Structural Variations and Photochromism via Light-Induced Fluorescence to Phosphorescence Switching.

Ultralong afterglow emissions due to room-temperature phosphorescence (RTP) are of paramount importance in the advancement of smart sensors, bioimaging and light-emitting devices. We herein present an efficient approach to achieve rarely accessible phosphorescence of heavy atom-free organoboranes via photochemical switching of sterically tunable fluorescent Lewis pairs (LPs). LPs are widely applied in and well-known for their outstanding performance in catalysis and supramolecular soft materials but have not thus far been exploited to develop photo-responsive RTP materials. The intramolecular LP M1BNM not only shows a dynamic response to thermal treatment due to reversible N→B coordination but crystals of M1BNM also undergo rapid photochromic switching. As a result, unusual emission switching from short-lived fluorescence to long-lived phosphorescence (rad-M1BNM, τRTP =232 ms) is observed. The reported discoveries in the field of Lewis pairs chemistry offer important insights into their structural dynamics, while also pointing to new opportunities for photoactive materials with implications for fast responsive detectors.

Dynamic B/N Lewis Pairs: Insights into the Structural Variations and Photochromism via Light‐Induced Fluorescence to Phosphorescence Switching

AbstractUltralong afterglow emissions due to room‐temperature phosphorescence (RTP) are of paramount importance in the advancement of smart sensors, bioimaging and light‐emitting devices. We herein present an efficient approach to achieve rarely accessible phosphorescence of heavy atom‐free organoboranes via photochemical switching of sterically tunable fluorescent Lewis pairs (LPs). LPs are widely applied in and well‐known for their outstanding performance in catalysis and supramolecular soft materials but have not thus far been exploited to develop photo‐responsive RTP materials. The intramolecular LP M1BNM not only shows a dynamic response to thermal treatment due to reversible N→B coordination but crystals of M1BNM also undergo rapid photochromic switching. As a result, unusual emission switching from short‐lived fluorescence to long‐lived phosphorescence (rad‐M1BNM, τRTP=232 ms) is observed. The reported discoveries in the field of Lewis pairs chemistry offer important insights into their structural dynamics, while also pointing to new opportunities for photoactive materials with implications for fast responsive detectors.

Switchable Circularly Polarized Signals with High Asymmetric Factor Triggered by Dual Photonic Bandgap Structure.

Currently, the smart photonic materials that can switch circularly polarized signals in real-time have attracted extensive attention due to numerous potential applications in information storage and photonics displays. However, the dynamically reversible switching of circularly polarized signals requires precise structural reconfiguration, which is rarely achieved in traditional biomaterials. Herein, a dual photonic bandgap (PBG) structure is constructed based on the optical propagation principle of cellulose-based photonic crystals, enabling the flexible switching of the intensity, wavelength, and direction of circularly polarized luminescence (CPL). By adjusting the fluorescence intensity and the matching degree of chiral structure, the asymmetric factor value of dual PBG structure is up to -1.47, far exceeding other cellulose-based materials. Importantly, it is demonstrated that dual CPL emission can be efficiently induced by two different PBGs, opening a new approach for on-demand switching of single and dual CPL emission. In addition, the dual PBG structure exhibits dual circularly polarized reflected signals under the circular polarizer, which perfectly embodies the applicability of multiple encryptions in QR codes. This work provides new insights into the real-time manipulation of circularly polarized signals by chiral photonic materials.

Methoxy substituent facilitated wide solvatofluorochromism, white light emission, polymorphism and stimuli-responsive fluorescence switching in donor-π-acceptor

Introducing methoxy substituent into triphenylamine-acetophenone based donor-π-acceptor fluorophore, 3-(4-(diphenylamino)phenyl)-1-phenylprop-2-en-1-one (1), produced strong solvatofluorochromism including white light emission, fluorescent polymorphs and mechano-responsive fluorescence switching. The unsubstituted and methoxy substituted compounds displayed strong solvent polarity mediated tunable emission in the solution. Interestingly, 3-(4-(diphenylamino)phenyl)-1-(4-methoxyphenyl)prop-2-en-1-one (2) and 3-(4-(diphenylamino)-2-methoxyphenyl)-1-(4-methoxyphenyl)prop-2-en-1-one (3) showed single molecule white light emission in DMSO and ethanol, respectively. 1-3 exhibited strong green/yellow fluorescence in the solid-state (Quantum yield (Φf) = 10 to 23%). 2 produced fluorescent polymorphs (green (2-G) and yellow (2-Y). Single crystal structural analysis revealed that donor and acceptor phenyl units adopted coplanar conformation in 2-G and 3 whereas twisted molecular conformation in 1 and 2-Y. Further, 2-G exhibited π…π interactions facilitated isolated dimers whereas 2-Y showed well separated molecules in the crystal lattice. Aggregation induced emission (AIE) studies showed morphological transformation induced fluorescence tuning for 2. The intramolecular charge transfer (ICT) from TPA to acetophenone was confirmed by computational studies. Mechanofluorochromic (MFC) studies of 1 showed only slight reduction of intensity without modulating fluorescence wavelength significantly but 2 and 3 exhibited visible emissive colour change from yellow to green and vice versa by crushing and heating. Both 2 and 3 also exhibited self-reversible fluorescence switching that was confirmed by PXRD pattern. Thus, methoxy group introduction resulted in obtaining white light emitting fluorescence molecules in the solution state and self-reversible fluorescence switching materials.

Recent Advances in Organic Room-Temperature Phosphorescence of Heteroatom (B/S/P)-Containing Chromophores

Recent Advances in Organic Room-Temperature Phosphorescence of Heteroatom (B/S/P)-Containing Chromophores

Highly Stable Switchable Emissions of an Erbium-Doped Fiber Ring Laser Using Cascaded MZIs Based on CHCF

A stable, single, and dual-wavelength erbium-doped fiber laser (EDFL), based on two Mach–Zehnder interferometers (MZIs), arranged in a cascade configuration, was proposed for experimental purposes. Both MZIs were assembled by splicing a capillary hollow-core fiber (CHCF) section between two multimode fibers (MMFs) segments. The novelty of this single and dual-wavelength EDFL is that the switchable operation of the laser is achieved by thermally tuning the interference pattern of one MZI and not by adjusting the polarization state inside the fiber ring cavity. The maximum measured value of SNR was 58.9 dB for the single and dual-wavelength laser emissions. Moreover, the stable output power exhibited by this EDFL, in terms of minimal power and wavelength fluctuations, at 0.05 dB and 10 pm, was detected during the single and dual-wavelength operation. It is worth noticing that switching is achieved at exact wavelength locations with a separation of 1.8 nm and not randomly, as reported by other works. These features make this switchable EDFL an appealing candidate for application in optical fiber communication systems and fiber sensing.

Ligands engineering of gold nanoclusters with enhanced photoluminescence for deceptive information encryption and glutathione detection

Gold nanoclusters (Au NCs) have appeared as an essential alternative to traditional quantum dots and fluorescent molecules for the development of intelligent stimuli-responsive photoluminescence (PL), but the low PL emission of Au NCs restricts their broad applications. Herein, we reported a simple yet effective strategy for preparing Au NCs with high PL by ligands engineering of 4-hydroxy-2-mercapto-6-methylpyrimidine (MTU) and L-Arginine (Arg). Owing to the rigidified shell and the ligand-to-metal charge transfer (LMCT) effects, it was found that the assembly of Arg ligand on MTU-protected Au NCs (Arg/MTU-Au NCs) led to a significantly enhanced PL in the alkaline solution up to 30 times. Moreover, utilizing the tunable LMCT, the Arg/MTU-Au NCs displayed rapid responses to multi-type ionic interaction in a reversible manner, such as H+/OH− and Cu2+/glutathione (GSH) pairs. Inspired by these intriguing ions-responsive LMCT and the associated switchable PL emission, the Arg/MTU-Au NCs were successfully used as excellent stimuli-responsive PL probes for intriguing deceptive information encryption and biosensing as well. This work would provide new insight into regulating the PL emission of Au NCs by ligands engineering and advance their potential applications in information encryption and bioassay.

Photoactive CuI-Cross-Linked Polyurethane Materials.

Using multinuclear copper iodide complexes as cross-linking agents in a polyurethane matrix, original photoluminescent stimuli-responsive materials were synthesized. The intrinsic photoluminescence properties of the covalently incorporated copper iodide complexes are thus transferred to the materials while retaining the beneficial characteristics of the polymer host. The transparent materials exhibit room-temperature phosphorescence with emission switching properties by displaying luminescence thermochromism and solvatochromism. The luminescence thermochromism is characterized by a change in the wavelength and intensity of the emission with temperature, and the vapochromic effect presents a contrasted response of extinction or exaltation according to the nature of the solvent of exposure. By combining the luminescence characteristics of photoactive copper iodide complexes with the ease of polymer processing, the application of these luminescent materials as phosphors in LED (light-emitting diode) devices was also demonstrated. The present study shows that the use of copper iodide complexes as cross-linkers in polymeric materials is a relevant strategy to design materials with enhanced functionalities in addition to their low cost and sustainable characteristics.